Neuronal Assembly Detection and Cell Membership Specification by Principal Component Analysis

In 1949, Donald Hebb postulated that assemblies of synchronously activated neurons are the elementary units of information processing in the brain. Despite being one of the most influential theories in neuroscience, Hebb's cell assembly hypothesis only started to become testable in the past two decades due to technological advances. However, while the technology for the simultaneous recording of large neuronal populations undergoes fast development, there is still a paucity of analytical methods that can properly detect and track the activity of cell assemblies. Here we describe a principal component-based method that is able to (1) identify all cell assemblies present in the neuronal population investigated, (2) determine the number of neurons involved in ensemble activity, (3) specify the precise identity of the neurons pertaining to each cell assembly, and (4) unravel the time course of the individual activity of multiple assemblies. Application of the method to multielectrode recordings of awake and behaving rats revealed that assemblies detected in the cerebral cortex and hippocampus typically contain overlapping neurons. The results indicate that the PCA method presented here is able to properly detect, track and specify neuronal assemblies, irrespective of overlapping membership

Does bone impaction technique reduce tunnel enlargement in ACL reconstruction?

The aim of this study was to investigate effects of bone impaction technique on tunnel enlargement after ACL reconstruction at a minimum 2 years follow-up. Two groups of patients who had been operated upon with the same arthroscopic technique with the exception of tibial tunnel constitution were compared. Twenty-one patients of group A (drilling to 6 mm followed enlargement to 8–9 mm by using dilators) and 23 patients of group B (directly drilling to the size of the graft) were evaluated clinically and radiographically based on multislice computerised tomography (MSCT) retrospectively. At follow-up, there was no statistical difference between tunnel diameters between two groups at the femoral site, but significant difference at the tibial site (p = 0.00192 for coronal; p = 0.0171 for sagittal diameter). Both groups were comparable according pre- and postoperative Lysholm and IKDC scores (p < 0.5 Mann-Whitney U test). Compacted tunnel walls may resist enlargement, suggesting this technique resulted in better tunnel diameter values especially with intratunnel fixation

Evaluation of tibial bone-tunnel changes with X-ray and computed tomography after ACL reconstruction using a bone-patella tendon-bone autograft

Thirteen patients who underwent anterior cruciate ligament (ACL) reconstruction with bone-patella tendon-bone autografts (BTB) using interference screws were the subjects of this study. We analysed the relationship between bone-tunnel changes and clinical results 2 years after ACL reconstruction. To investigate changes, X-ray images were used to evaluate bone-tunnel enlargement, and computed tomography (CT) was used to evaluate the sclerotic area around the bone tunnel. The KT-2000 was used to measure the discrepancy of tibial anterior displacement between the affected and nonaffected sides (DTAD). There was no correlation between bone-tunnel enlargement and DTAD. On the other hand, in the CT evaluation, there was a significant correlation between the sclerotic area and DTAD. Our results suggest that it is more significant to analyse the area of sclerotic change than bone-tunnel enlargement for clinical evaluation. We cannot evaluate bone-tunnel changes correctly with two-dimensional X-rays and cannot analyse the sclerotic area using X-rays. Therefore, we recommend that CT, with which it is possible to analyse the sclerotic area, be used to evaluate bone-tunnel changes and clinical results

Bone tunnel enlargement after ACL reconstruction using autologous hamstring tendons: a CT study

Purpose: To evaluate prospectively the increase in the size of the tibial and femoral bone tunnel following arthroscopic anterior cruciate ligament (ACL) reconstruction with quadrupled-hamstring autograft. Methods: Twenty-five consecutive patients underwent arthroscopic ACL reconstruction with quadrupled-hamstring autograft. Preoperative clinical evaluation was performed using the Lysholm knee score, Tegner activity level, and International Knee Documentation Committee forms and a KT-1000 arthrometer (side to side). Computed tomography (CT) of the femoral and tibial tunnel was performed on the day after operation in all cases and at mean follow-up of 10 months (range 9–11 months).Results: All of the clinical evaluation scales performed showed an overall improvement. The postoperative anterior laxity difference was <3 mm in 16 patients (70%) and 3–5 mm in seven patients (30%). The mean average femoral tunnel diameter increased significantly (3%) from 9.04±0.05 mm postoperatively to 9.3±0.8 mm at 10 months; tibial tunnel increased significantly (11%) from 9.03±0.04 mm to 10±0.8 mm. There were no statistically significant differences between tunnel enlargement, clinical results, and arthrometer evaluation. Conclusions: The rate of tunnel widening observed in this study seems to be lower than that reported in previous studies that used different techniques. We conclude that an anatomical surgical technique and a less aggressive rehabilitation process influenced the amount of tunnel enlargement after ACL reconstruction with doubled hamstrings